There are certain industrial applications where conduits are used to carry solid material such as pulverized coal. In such conduits erosion is a problem where the solids are abrasive. For example, when pulverized coal is conveyed through a conduit, erosion can be excessive when certain kinds of coal are used.
The entire wall of a solids conveying conduit is susceptible to erosion. Certain portions of the conduit, however, are more susceptible to erosion than others. Where the conduit curves, the abrasive solids tend to erode the outer periphery of the curve because they impinge against the conduit at that location.
Use of a conduit over a period of years to convey abrasive solids will actually wear holes through the side wall of the conduit. This will cause a loss of material. Further, it makes for a dirty environment for the workers and can create an unsafe condition. For example, in a power plant where pulverized coal is conveyed through a conduit and there is a hole through the side wall, coal dust will be ever present in the surrounding area creating a fire hazard and an unhealthy work area for the workers. In addition, considerable expense is incurred because of the constant clean-up operation which becomes necessary.
Attempts have been made to prevent further leakage once the side wall of a conduit fails. Plates have been welded in place or held against the leaky conduit by bands passing over the plate and around the conduit. Such attempts have not been satisfactory for several reasons. For one, crevices between the plate and conduit are present and allow some of the solid material to leak out. Further, such repairs result in an inner wall which is not smooth and which is therefore more susceptible to erosion than a conduit which has not been repaired. Because it is expensive to replace conduits and the plates tend to wear more quickly than the unpatched portion of the conduit, it is not uncommon for a plate used to patch a conduit to fail because a hole wears through it. Additional plates are then applied to the leaking plates in an attempt to prevent for a time further leakage of solid material. This creates an even more irregular inner surface; and therefore, the additional plates prevent leakage for a shorter time than do the original plates.
Patching leaky conduits with plates is also unsatisfactory because the conduits tend to vibrate; and therefore, the plates will tend to loosen and have to be tightened or welded from time to time if they are to have any substantial effect in preventing leakage of solids.